For one cell to support large capacity group communication of thousands of people or more via a group communication service such as Push-To-Talk (PTT) or Push-To-All (PTA) in a WiMAX network, the following two requirements are needed. For convenience in description, the PTA as a representative of a group communication service is exemplarily described.
(1) A group communication packet should be transmitted to a terminal in a multicast method on a radio link. That is, all terminals should receive one time of packet transmission by a base station.
(2) A terminal should receive a group communication packet in an idle state. Since a terminal uses a radio resource and a resource inside a base station in an awake state, the terminal should maintain an idle state to avoid this.
Currently, various kinds of services use a Keep Alive method in order to manage an access state of a terminal. However, since a terminal should have a Connection ID (CID) in order to transmit a packet for Keep Alive (that is, a packet for access state transfer) and an idle state is a state to which a CID has not been allocated, the terminal should make a transition to an awake state to obtain a CID. This is contradictory to a requirement that the terminal should maintain an idle state for large capacity group communication. In addition, since a Keep Alive packet is transmitted in an awake state and so the number of users of group communication is limited to a level of hundreds of people regardless of whether a group communication service is a multicast method, it is difficult to support the large capacity group communication service where more than thousands of people perform reception simultaneously.
When a multicast group communication starts/ends or a handover is performed, a PTA path for packet transmission belonging to relevant group communication is established/released between a Base Station (BS) to which a relevant terminal belongs and an Access Service Network Gate Way (ASN-GW). At this point, when a certain abnormal state occurs, a mismatch may be generated to path establishment/release states managed by the BS and the ASN-GW, respectively. To determine whether this mismatch exists and resolve this mismatch, whether abnormality is generated to a transmission path establishment/release state between the BS and the ASN-GW should be known, and for this purpose, the BS should monitor whether a group communication receive terminal exists in a relevant cell. Currently, for this monitoring, a terminal directly communicates with a PTA server or an ASN-GW to perform a Keep Alive procedure. However, in the case where the terminal directly communicates with the PTA server or the ASN-GW to perform the Keep Alive procedure, as a group communication scale increases, a big load may be applied to the PTA server or the ASN-GW.